Magnetic recording and reproducing apparatuses, represented by magnetic disk drives, have been required to provide higher data transfer rates and higher recording densities. Raising the data transfer rate requires a higher recording frequency, causing a tendency to increase after-write read noise. The term “after-write read noise” used herein means a phenomenon in which after data is recorded on the magnetic disk, noise is produced on the read output during the subsequent read operation. A conventional method for preventing the thin film magnetic head from outputting after-write noise, is to control the thickness and magnetic property, namely magnetostrictive coefficient λ of the upper magnetic shield disposed above the magnetic sensor film of the read head.
In Japanese Laid-Open Patent No. 2001-291211 (“Patent Document 1”), there is disclosed a thin film magnetic head in which the composition and magnetostrictive coefficient λ of the upper magnetic shield is controlled in its film thickness direction in order to reduce after-write read noise.
For magnetic disk drives to further advance in data transfer rate and recording density, it is necessary to suppress after-write read noise which tends to increase as the data transfer rate and recording density are raised. The magnetic shield is made of Permalloy (Ni80Fe20) and has large crystal grains of 50 nm or larger in diameter. After-write read noise is attributable to disturbance of the magnetic domain structure which depends on these crystal grains. In particular, it is considered that as the read track width approaches to 100 nm, contribution of the crystal grain size to such noise becomes significant, making it necessary to control the size of crystal grains constituting the magnetic shield film.